Air conditioner

Abstract

An air conditioner includes: an outdoor fan provided in an outdoor unit; a permanent magnet synchronous motor that drives the outdoor fan; an inverter that uses a DC power source as a power source and applies a voltage to the permanent magnet synchronous motor; an inverter control means that controls the output voltage of the inverter; and a shunt resist connected between the DC power source and the inverter. If the outdoor fan is rotating due to an external force while the inverter is stopped, the inverter control means causes the inverter to operate using a brake sequence that brakes the rotation of the outdoor fan, and then causes the inverter to operate using a drive sequence that power-drives the outdoor fan.

The invention claimed is: 
     
       1. An air conditioner in which an indoor device and an outdoor device are separately provided, the air conditioner comprising:
 an outdoor fan that is provided in the outdoor device; 
 a permanent magnet synchronous motor that drives the outdoor fan; 
 an inverter of which power is supplied from a direct-current power supply and which applies a voltage to the permanent magnet synchronous motor; 
 an inverter control unit that controls a voltage output from the inverter; 
 a current detection unit that is connected between the direct-current power supply and the inverter; and 
 a protection circuit that detects a current flowing through the current detection unit and executes a protection thereof, 
 wherein 
 the inverter control unit includes a brake sequence that brakes a rotation of the outdoor fan, and 
 the brake sequence sets a starting-time conduction ratio, which is a conduction ratio at a time of starting braking, such that the protection circuit is able to detect the current flowing through the current detection unit. 
 
     
     
       2. The air conditioner according to  claim 1 , wherein
 the inverter control unit has a drive sequence in which the inverter is operated by the brake sequence, and thereafter the outdoor fan is run on a power running, and 
 the drive sequence changes an output voltage and a conduction phase of the inverter based on information on a rotation number of the outdoor fan during an operation of the brake sequence. 
 
     
     
       3. The air conditioner according to  claim 1 , wherein
 in the brake sequence, a control of performing a line-to-line open circuit and a line-to-line short-circuit of the permanent magnet synchronous motor is executed based on information on a conduction ratio, wherein 
 the information on a conduction ratio is set such that a time period of short circuit becomes longer along with a time lapse of brake control and is set so as to be in a range from the starting-time conduction ratio to an ending-time conduction ratio which is a conduction ratio at a time of ending braking. 
 
     
     
       4. The air conditioner according to  claim 1 , wherein
 in the brake sequence, when a rotation number of the outdoor fan is unable to be braked to equal to or less than a driving-permission rotation number, the braking is stopped, and 
 then the braking is performed again after a certain period of time has lapsed. 
 
     
     
       5. The air conditioner according to  claim 1 , wherein
 when a rotation number of the outdoor fan becomes equal to or larger than a driving-permission rotation number, it is determined that sufficient heat exchange can be performed in the outdoor device and the brake sequence shifts to a standby mode, and 
 when the rotation number becomes equal to or less than the driving-permission rotation number, a braking operation is performed. 
 
     
     
       6. The air conditioner according to  claim 1 , wherein
 among semiconductor switching elements constituting the inverter, one set of elements connected to a positive side or a negative side of the direct-current power supply is constituted from normally-on switching elements, and 
 the brake sequence maintains the inverter in a stopped state. 
 
     
     
       7. The air conditioner according to  claim 1 , wherein
 the inverter control unit has a drive sequence in which the inverter is operated by the brake sequence, and thereafter the outdoor fan is run on a power running, and 
 when the braking of causing a rotation number of the outdoor fan to be equal to or less than a driving-permission rotation number is completed, the brake sequence is ended and is shifted to the drive sequence. 
 
     
     
       8. The air conditioner according to  claim 1 , wherein
 semiconductor switching elements constituting the inverter are formed from a wide bandgap semiconductor. 
 
     
     
       9. The air conditioner according to  claim 1 , wherein
 in the inverter, a wide bandgap semiconductor is used only for paths in which a current flows at the time of the short-circuit operation. 
 
     
     
       10. The air conditioner according to  claim 2 , wherein
 the drive sequence, in a case where the rotation number of the outdoor fan during an operation of the brake sequence is high, increases an applied voltage and a conduction phase at a time of activation. 
 
     
     
       11. The air conditioner according to  claim 3 , wherein
 an increment from the starting-time conduction ratio to the ending-time conduction ratio is large at a time of outputting the starting-time conduction ratio, and 
 the increment becomes smaller as a time lapse approaches a time of outputting the ending-time conduction ratio. 
 
     
     
       12. The air conditioner according to  claim 3 , wherein
 in the brake sequence, the starting-time conduction ratio is set according to a current detection speed of the current detection unit. 
 
     
     
       13. The air conditioner according to  claim 12 , wherein
 when the current detection speed is slow, the starting-time conduction ratio is set such that a time period of short circuit is long. 
 
     
     
       14. The air conditioner according to  claim 3 , wherein
 at a time of ending the brake sequence, the ending-time conduction ratio is set such that a short-circuit operation is a steady operation. 
 
     
     
       15. The air conditioner according to  claim 8 , wherein
 the wide bandgap semiconductor is made of silicon carbide, gallium nitride, or diamond. 
 
     
     
       16. The air conditioner according to  claim 9 , wherein
 the wide bandgap semiconductor is made of silicon carbide, gallium nitride, or diamond.